The present invention relates to a hydraulic system for a torque converter with a lock-up clutch.
A known hydraulic system for a torque converter with a lock-up clutch is illustrated on page 33 of a publication entitled "TOYOTA VISTA E-SV10 SERIES A/T MOUNTED CAR, NEW CAR INTRODUCTION MANUAL, JUL. 1982."In this known system, the lock-up clutch extends inside the converter chamber and defines on one side an apply chamber and on the opposite side a release chamber. A lock-up control valve is disposed between a pressure regulator valve and the torque converter to allow supply of hydraulic fluid to the release chamber and discharge of hydraulic fluid from the apply chamber in response to the absence of a lock-up, clutch engagement demand. In the presence of the lock-up clutch engagement demand, the lock-up control valve switches to allow supply of hydraulic fluid to the apply chamber and discharge of hydraulic fluid from the release chamber. In the former case, the lock-up clutch is released, while in the latter case the lock-up clutch is engaged. In order to keep hydraulic fluid pressure within the torque converter low enough in view of the structural rigidity of the torque converter, a pressure relief valve is provided between the pressure regulator valve and the lock-up control valve. With this pressure relief valve, the pressure of hydraulic fluid supplied to the torque converter via the lock-up control valve is prevented from increasing above a predetermined value. This means that the hydraulic fluid pressure within the torque converter remains unchanged regardless of whether the lock-up clutch is engaged or released.
In this known hydraulic system, since there is a limit to hydraulic fluid pressure allowed to be increased within the torque converter, the torque transmission capacity of the lock-up clutch is determined by this hydraulic fluid pressure within the torque converter. Thus, the torque transmission capacity of the lock-up clutch cannot be increased even if it is desired to increase torque transmission capacity. A conventional approach to this problem has been to use a torque converter with an increased diameter which allows the provision of a lock-up clutch having an increased frictional area.
An object of the present invention is to solve the above-mentioned problem without increasing the size or structural rigidity of a torque converter.
A specific object of the present invention is to improve a hydraulic system for a torque converter with a lock-up clutch such that, without any substantial change in the component parts, the torque transmission capacity of the lock-up clutch is increased.
Another object of the present invention is to provide a hydraulic control system for a torque converter with a lock-up clutch which can be adjusted to an engine capable of producing a large torque without any substantial change in component parts.